1. Field of the Invention
The present invention relates generally to a valve timing controller, a valve timing control method and an engine control unit for an internal combustion engine, and more particularly, to a valve timing controller, a valve timing control method and an engine control unit for an internal combustion engine which is equipped with a valve timing changing mechanism for changing a valve timing for at least one of an intake valve and an exhaust valve such that the engine is operated in a combustion mode switched between a uniform combustion mode in which a fuel injection is performed during an intake stroke and a stratified combustion mode in which a fuel injection is performed in a compression stroke.
2. Description of the Prior Art
A conventional valve timing controller for an internal combustion engine of the type mentioned above is known, for example, from Laid-open Japanese Patent Application No. 7-301144. An internal combustion engine described in this document comprises a cam phase changing mechanism which changes the phase of an intake cam (hereinafter referred to as the xe2x80x9ccam phasexe2x80x9d) for a crank shaft as a valve timing changing mechanism. A change in the cam phase results in a change in valve timing of an intake valve, i.e., overlapping of the intake valve with an exhaust valve, and so on, thereby leading to a change in a filling efficiency and internal EGR. The disclosed valve timing controller sets a target cam phase in accordance with the engine rotational speed and a load represented by a throttle valve opening, so that the cam phase is controlled to reach the target cam phase, thereby achieving engine power suitable for the load of the internal combustion engine, and an improvement in the exhaust gas characteristics.
Another known valve timing controller for an internal combustion engine is described, for example, in Japanese Patent No. 2630632. The disclosed internal combustion engine comprises a cam profile switching mechanism, as a valve timing changing mechanism, which has an intake cam and an exhaust cam comprised of a lower speed cam and a higher speed cam, respectively, having different cam profiles from each other, such that the cam profile of each cam is switched between the lower speed cam and the higher speed cam. The switching of the cam profile causes a change in valve timings of the intake valve and the exhaust valve, i.e., the amount of valve lift and so on, resulting in an change in the filling efficiency. In this valve timing controller, the cam profile is switched based on the engine rotational speed and a basic fuel injection time which is calculated based on the engine rotational speed and a load represented by an intake pipe inner pressure, thereby providing engine power suitable for the load of the internal combustion engine.
Further, a recent internal engine, known as a direct injection type, directly injects a fuel into a cylinder, and is operated in a combustion mode which is switched between a uniform combustion mode and a stratified combustion mode in order to improve the fuel economy (see, for example, Laid-open Japanese Patent Application No. 11-22508). In this internal combustion engine, the stratified combustion mode is performed during an extremely low load operation such as idling, wherein a fuel injection is performed during an intake stroke with a throttle valve being substantially fully opened to supply a large amount of intake air into a cylinder for burning at an extremely leaner air/fuel ratio than the stoichiometric air/fuel ratio. On the other hand, the uniform combustion mode is performed during operations other than the extreme low load operation, wherein a fuel injection is performed during a compression stroke, and a throttle valve opening is controlled in accordance with a load represented by the engine rotational speed and an accelerator opening to control the amount of intake air for burning at a richer air/fuel ratio than the stratified combustion mode.
The foregoing cam phase changing mechanism and profile switching mechanism, though contributing to the improvement on the exhaust gas characteristics and engine power, may experience problems as follows, if they are employed in the conventional direct injection type internal combustion engine. As described above, the direct injection type internal combustion engine substantially fully opens the throttle valve during an extremely low load operation such as idling to perform the stratified combustion mode with a large amount of intake air supplied into a cylinder, so that the throttle valve opening, absolute intake pipe inner pressure, and amount of intake air become extremely large, causing the internal combustion engine to exhibit behaviors exactly opposite to those of a normal intake port injection type internal combustion engine. On the other hand, the conventional cam phase changing mechanism sets its target cam phase in accordance with the throttle valve opening as a parameter that represents the load, while the cam profile switching mechanism switches the cam profile in response to the intake pipe inner pressure that represents the load. Thus, if such a valve timing changing mechanism is simply combined in the conventional direct injection type internal combustion engine, a valve timing suitable for a load cannot be set in the stratified combustion mode, and as a result, the engine fails to ensure required engine power and internal EGR, resulting in deteriorated exhaust gas characteristics, fuel economy and operability.
The present invention has been made to solve the problem as mentioned above, and its object is to provide a valve timing controller, a valve control method and an engine control unit suitable for use in a direct injection type internal combustion engine, which are capable of appropriately setting a valve timing in accordance with an engine load even in the stratified combustion mode.
To achieve the above object, according to a first aspect of the present invention, there is provided a valve timing controller for an internal combustion engine which is equipped with a valve timing changing mechanism for changing a valve timing of at least one of an intake valve and an exhaust valve so that the engine is operated in a combustion mode switched between a uniform combustion mode in which a fuel is injected into a cylinder during an intake stroke and a stratified combustion mode in which a fuel is injected into a cylinder in a compression stroke.
The valve timing controller according to the first aspect is characterized by comprising engine rotational speed detecting means for detecting a rotational speed of the internal combustion engine; accelerator pedal opening detecting means for detecting an opening of an accelerator pedal; required torque determining means for determining a required torque outputted by the internal combustion engine based on the detected engine rotational speed and accelerator pedal opening; and valve timing determining means for determining the valve timing in accordance with the determined required torque and the engine rotational speed.
The internal combustion engine is operated in the combustion mode which is switched between the uniform combustion mode in which a fuel is injected into a cylinder in an intake stroke and the stratified combustion mode in which the fuel is injected in a compression stroke. Also, according to the valve timing controller in the first aspect of the present invention, a required torque outputted by the internal combustion engine is determined based on the detected engine rotational speed and accelerator pedal opening, and a valve timing for the intake valve and/or the exhaust valve is determined in accordance with the determined required torque and engine rotational speed. In this way, the valve timing is determined in accordance with the required torque and engine rotational speed, while the required torque is determined as a torque which should be outputted by the internal combustion engine, based on the engine rotational speed and the accelerator pedal opening which represents a load on the engine. It is therefore possible to set the valve timing in accordance with the required torque, i.e., the load, and to appropriately set the valve timing in accordance with the load without affected by the throttle valve opening, intake pipe inner pressure, amount of intake air, and so on, even in the stratified combustion mode. As a result, the filling efficiency can be appropriately controlled to ensure required engine power.
To achieve the above object, according to a second aspect of the present invention, there is provided a valve timing controller for an internal combustion engine having a valve timing changing mechanism for changing a valve timing of at least one of an intake valve and an exhaust valve so that the engine is operated in a combustion mode switched between a uniform combustion mode in which a fuel is injected into a cylinder during an intake stroke and a stratified combustion mode in which a fuel is injected into a cylinder in a compression stroke.
The valve timing controller according to the second aspect of the present invention is characterized by comprising an engine rotational speed detecting module for detecting a rotational speed of the internal combustion engine; an accelerator pedal opening detecting module for detecting an opening of an accelerator pedal; a required torque determining module for determining a required torque outputted by the internal combustion engine based on the detected engine rotational speed and accelerator pedal opening; and a valve timing determining module for determining the valve timing in accordance with the determined required torque and the engine rotational speed.
This valve timing controller provides the same advantageous effects as described above concerning the valve timing controller according to the first aspect of the present invention.
To achieve the above object, according to a third aspect of the present invention, there is provided a valve timing control method for an internal combustion engine having a valve timing changing mechanism for changing a valve timing of at least one of an intake valve and an exhaust valve so that the engine is operated in a combustion mode switched between a uniform combustion mode in which a fuel is injected into a cylinder during an intake stroke and a stratified combustion mode in which a fuel is injected into a cylinder in a compression stroke.
The valve timing control method according to the third aspect of the present invention is characterized by comprising the steps of detecting a rotational speed of the internal combustion engine; detecting an opening of an accelerator pedal; determining a required torque outputted by the internal combustion engine based on the detected engine rotational speed and accelerator pedal opening; and determining the valve timing in accordance with the determined required torque and the engine rotational speed.
This control method provides the same advantageous effects as described above concerning the valve timing controller according to the first aspect of the present invention.
To achieve the above object, according to a fourth aspect of the present invention, there is provided an engine control unit including a control program for causing a computer to carry out control of valve timing for an internal combustion engine having a valve timing changing mechanism for changing a valve timing of at least one of an intake valve and an exhaust valve so that the engine is operated in a combustion mode switched between a uniform combustion mode in which a fuel is injected into a cylinder during an intake stroke and a stratified combustion mode in which a fuel is injected into a cylinder in a compression stroke.
The engine control unit according to the fourth aspect of the present invention is characterized in that the control program causes the computer to detect a rotational speed of the internal combustion engine; detect an opening of an accelerator pedal; determine a required torque outputted by the internal combustion engine based on the detected engine rotational speed and accelerator pedal opening; and determine the valve timing in accordance with the determined required torque and the engine rotational speed.
This engine control unit provides the same advantageous effects as described above concerning the valve timing controller according to the first aspect of the present invention.
In the valve timing controller, preferably, the valve timing changing mechanism includes a cam phase changing mechanism for changing a cam phase, with respect to a crank shaft, of at least one of an intake cam for opening and closing the intake valve and an exhaust cam for opening and closing the exhaust valve; and the valve timing determining means includes target cam phase determining means for determining a target cam phase for the cam phase in accordance with the required torque and the engine rotational speed.
With the configuration described above, the target cam phase for the intake cam and/or the exhaust cam is determined in accordance with the required torque and engine rotational speed, and the actual cam phase is variably controlled aiming at the target cam phase, so that the cam phase can be appropriately controlled in accordance with the load to appropriately control the filling efficiency and inner EGR, thereby making it possible to ensure required engine power and improve the exhaust gas characteristics.
Also, in the valve timing controller, preferably, the valve timing changing mechanism includes a cam phase changing mechanism for changing a cam phase, with respect to a crank shaft, of at least one of an intake cam for opening and closing the intake valve and an exhaust cam for opening and closing the exhaust valve, and the valve timing determining module includes a target cam phase determining module for determining a target cam phase for the cam phase in accordance with the required torque and the engine rotational speed.
This preferred embodiment of the valve timing controller provides the same advantageous effects as provided by the corresponding preferred embodiment of the valve timing controller.
Also, in the valve timing control method for an internal combustion engine, preferably, the valve timing changing mechanism includes a cam phase changing mechanism for changing a cam phase, with respect to a crank shaft, of at least one of an intake cam for opening and closing the intake valve and an exhaust cam for opening and closing the exhaust valve, wherein the step of changing a valve timing includes changing a cam phase, with respect to a crank shaft, of at least one of an intake cam for opening and closing the intake valve and an exhaust cam for opening and closing the exhaust valve, and the step of determining the valve includes determining a target cam phase for the cam phase in accordance with the required torque and the engine rotational speed.
This preferred embodiment of the control method provides the same advantageous effects as provided by the corresponding preferred embodiment of the valve timing controller.
Also, in the engine control unit, preferably, the valve timing changing mechanism includes a cam phase changing mechanism for changing a cam phase, with respect to a crank shaft, of at least one of an intake cam for opening and closing the intake valve and an exhaust cam for opening and closing the exhaust valve, and when the control program causes the computer to determine the valve timing, the control program causes the computer to determine a target cam phase for the cam phase in accordance with the required torque and the engine rotational speed.
This preferred embodiment of the engine control unit provides the same advantageous effects as provided by the corresponding preferred embodiment of the valve timing controller.
Preferably, in the valve timing controller, the valve timing changing mechanism includes a cam profile switching mechanism for switching at least one of an intake cam for opening and closing the intake valve and an exhaust cam for opening and closing the exhaust valve to one of a plurality of cams having different cam profiles from each other; and the valve timing determining means includes cam profile switching means for switching the cam profile in accordance with the required torque and the engine rotational speed.
With the configuration described above, since the cam profile for the intake cam and/or the exhaust cam is switched in accordance with the required torque and engine rotational speed, the cam profile can be appropriately switched in accordance with the load, thereby making it possible to ensure required engine power.
Preferably, in the valve timing controller, the valve timing changing mechanism includes a cam profile switching mechanism for switching at least one of an intake cam for opening and closing the intake valve and an exhaust cam for opening and closing the exhaust valve to one of a plurality of cams having different cam profiles from each other; and the valve timing determining module includes a cam profile switching module for switching the cam profile in accordance with the required torque and the engine rotational speed.
This preferred embodiment of the valve timing controller provides the same advantageous effects as provided by the corresponding preferred embodiment of the valve timing controller.
Preferably, in the valve timing control method for an internal combustion engine, the valve timing changing mechanism includes a cam profile switching mechanism for switching at least one of an intake cam for opening and closing the intake valve and an exhaust cam for opening and closing the exhaust valve to one of a plurality of cams having different cam profiles from each other, and the step of determining the valve timing includes switching the cam profile in accordance with the required torque and the engine rotational speed.
This preferred embodiment of the control method provides the same advantageous effects as provided by the corresponding preferred embodiment of the valve timing controller.
Preferably, in the engine control unit, the valve timing changing mechanism includes a cam profile switching mechanism for switching at least one of an intake cam for opening and closing the intake valve and an exhaust cam for opening and closing the exhaust valve to one of a plurality of cams having different cam profiles from each other, and when the control program causes the computer to determine the valve timing, the control program causes the computer to switch the cam profile in accordance with the required torque and the engine rotational speed.
This preferred embodiment of the engine control unit provides the same advantageous effects as provided by the corresponding preferred embodiment of the valve timing controller.
Preferably, the valve timing controller further includes at least one of engine temperature detecting means for detecting the temperature of the internal combustion engine and vehicle speed detecting means for detecting the speed of a vehicle which carries the internal combustion engine, and valve timing correcting means for correcting the valve timing in accordance with at least one of the detected engine temperature and vehicle speed.
As the temperature or the vehicle speed of the internal combustion engine changes, the effective filling efficient varies due to a change in the density of intake air or the like. Therefore, according to the present invention, the valve timing is corrected by the temperature and/or vehicle speed of the internal combustion engine to compensate for a deviation of the filling efficiency, thereby making it possible to provide more proper engine power.
Preferably, the valve timing controller further includes at least one of an engine temperature detecting module for detecting the temperature of the internal combustion engine and a vehicle speed detecting module for detecting the speed of a vehicle which carries the internal combustion engine, and a valve timing correcting module for correcting the valve timing in accordance with at least one of the detected engine temperature and vehicle speed.
This preferred embodiment of the valve timing controller provides the same advantageous effects as provided by the corresponding preferred embodiment of the valve timing controller.
Preferably, the valve timing control method further includes the steps of detecting at least one of a temperature of the internal combustion engine and a speed of a vehicle equipped with the internal combustion engine; and correcting the valve timing in accordance with at least one of the detected engine temperature and vehicle speed.
This preferred embodiment of the control method provides the same advantageous effects as provided by the corresponding preferred embodiment of the valve timing controller.
Preferably, in the engine control unit, the control program further causes the computer to detect at least one of a temperature of the internal combustion engine and a speed of a vehicle equipped with the internal combustion engine; and to correct the valve timing in accordance with at least one of the detected engine temperature and vehicle speed.
This preferred embodiment of the engine control unit provides the same advantageous effects as provided by the corresponding preferred embodiment of the valve timing controller.
Preferably, the internal combustion engine further includes a fuel injection valve for injecting the fuel which is disposed in a central portion of a top wall of a combustion chamber of the cylinder for injecting the fuel toward a recess formed in a piston. According to this preferred embodiment, the advantageous effects provided by the valve timing controller, the valve timing control method and the engine control unit according to the first through fourth aspects of the present invention and their preferred embodiments described above can be obtained in an optimized manner.